Has anybody else run into this problem? I've done two installations of
Cygwin/X on Windows 10 systems this week, and they both had problems
with the XWin Server dying just a few seconds after starting up. I
traced the problem back to xwin-xdg-menu.exe getting a Segmentation
fault, which then causes XWin Server to exit. I hacked an alternate
.startxwinrc file to prevent XWin Server from dying (it ends with a
"sleep infinity"), so I could debug it further.

With the XWin Server running reliably, I then ran "strace
xwin-xdg-menu.exe" and saw that it got a segmentation fault just after
reading a TTF font from the Windows Font directory (bahnschrift.ttf if
it matters). I noticed there were two recent library updates related to
font handling, so I tried back out to the previous version for each. It
turns out that when I reverted to version 1.7.4-1 of libharfbuzz0,
xwin-xdg-menu.exe stopped crashing.

If it matters, both these systems are the Fall Creator's Update (1709)
of Windows 10 64-bit, and I'm running the 32-bit version of Cygwin.

Hopefully someone can track down and fix this recent bug!

Thanks for reporting this.
I can reproduce this problem, but it only seems to occur with 32-bit cygwin.

(Obviously you also need a recent enough Windows 10 to have the
Bahnschrift font)

The actual crash seems to be in fontconfig, e.g. 'fc-query
/usr/share/fonts/microsoft/bahnschrift.ttf' fails in the same way.

I didn't get very far investigating the problem, as rebuilding the
fontconfig package with the current toolchain seems to be enough to make
the problem go away.